The Solar System

Planetary Systems

What are protoplanets?

Protoplanets are early solar system objects that range in size from about sixty to six thousand miles (one hundred to ten thousand kilometers) across. Again, like the term “planetesimal” and many other terms in science, this is not an exact definition. More generally, protoplanets are objects in the protoplanetary nebula that are large enough that they are growing in size and mass by attracting other, smaller objects with their gravitational pull.